1. Field of the Invention
The present invention is in general concerned with a system for improving visibility in vehicles.
Poor visibility at night is a strenuous and dangerous condition, which causes anxiety in many vehicle operators. As a consequence of the poor visibility, the occurrences of accidents is significantly higher at night, in comparison to vehicle operation in the daytime under good visibility. Herein the difficulties with night visibility can be categorized as follows:
The range of visibility when facing headlights of oncoming vehicles is not far, and is over-estimated by many vehicle operators. This results in a too late a recognition of non-illuminated obstacles, pedestrians, bicycles without lights and of animals, and therewith to accidents.
The vehicle operator is blinded by the headlights of oncoming vehicles and their reflections, above all in the case of wet roads, and the vehicle is for a short period of time operating in a xe2x80x9cblack hole.xe2x80x9d Operators with night blindness and older vehicle operators are particularly susceptible because of their lower visual acuity.
In rain, fog and drifting snow, the visibility conditions can again be significantly worsened.
2. Description of the Related Art
An improvement of visibility at night is provided by an optoelectronic system which as set forth in DE-A-40 07 646. This system records a video image of a scene and presents it in enhanced or optimized form to the vehicle operator. The represented image shows substantially more than the vehicle operator can see with his own eyes directly through the windshield.
The system known from DE-A-40 07 646 contains, in addition to the conventional headlights, two xe2x80x9claser headlightsxe2x80x9d, which use near infrared emitting laser diodes as the light source. The laser diodes are driven pulsed with a pulse length of for example 50-100 xcexcs and a pulse interval of 100-1000 xcexcs. Therein the illumination of the scene can occur with a strip or with a point shaped pattern, whereby a plastic accentuation of the illuminated objects such as, for example, automobiles as distinguished from the road surface, can be achieved. A CCD-camera recording the video image is incorporated in the roof area of the vehicle. The CCD-camera includes an electronic shutter, which is synchronized with the laser diodes for avoidance of interferences or disturbances. By the synchronization of the CCD-camera with the emitting laser diodes it can be ensured that only light from the strips or surfaces illuminated by the laser diodes are used for the image construction, and that received light which has been diffused and received from other angular directions does not interfere. The details of the synchronization are described in DE-A-40 07 646 and are not repeated herein to avoid unnecessary repetition.
According to DE-A-40 07 646 an optical bandpass filter is provided in front of the camera objective or lense. The video image is displayed to the vehicle operator on a LCD-image screen. The utilization of laser light as described in DE-A-40 07 646 has a number of advantages. The laser emits in the wavelength of 800-2000 nm, preferably 810 nm in the near infrared. Since the infrared light is almost invisible to the human eye, illumination can be continuous wide open without restriction.
By using laser light, the glare or blinding of the camera by the visible headlights of oncoming vehicles can be substantially reduced. On the one hand the laser light possess a spectral breadth of only a few nm, while visible light sources such as halogen lights are hundreds of nm wide. If one provides an optical bandpass filter with a narrow pass breadth in front of the camera objective, then almost the entire laser light is emitted, while the light of oncoming vehicles is attenuated by a factor of 50-100. On the other hand, the laser diodes respond immediately to the driver current, and they can thus be pulsed rapidly in a simple manner. If one employs a video camera with a rapid electronic shutter, which is synchronized with the lasers, then the light of oncoming vehicles can be even further reduced.
A problem occurs however when two night visibility systems of this type with permanently operational laser headlights encounter each other. In DE 4007646 A1 the problem was solved in that the laser headlights of all vehicles emit with the same polarization, for example vertical polarization and in front of the camera objective or lens a thereto perpendicular analyzer or polarizer is present.
A disadvantage in the employment of polarizers and analyzers is however the weakening of the depolarized light reflected from the objects through the analyzer, which generally involves a factor of 2 to 4.
A device for a glare-free guidance of vehicles in traffic is known from DE 2001086 C3. A screen with variable light transmitivity is provided in the field of vision of the vehicle driver and the headlights are provided with flashlight sources. The light transmitivity of the screen is controlled electrically with a predetermined pulse frequency via a control device and varied between almost full transmitivity and strongly reduced light transmitivity.
From the publication DE 3836095 A1 a device is known for glare-free guidance of vehicles in traffic, in which likewise in the field of vision of the vehicle driver a screen is provided, with a light transmitivity which is controllable via a control device with a predetermined pulse frequency. This device also includes headlights for permanent emanation of pulsed infrared light. The control device is connected to a photo-electric receiver, which is so arranged, that it recognizes light emitted by an oncoming vehicle as foreign light and in the case of occurrence of pulsed foreign light so controls the screen and headlights that they are synchronized and in opposition to the pulsed foreign light, in such a manner, that respectively with high light emission of the foreign light the light transmitivity of the screen and the light emission of headlights are reduced.
It is thus the task of the present invention to make available a system for improvement of visibility in vehicles, which suppresses the emitted light from oncoming vehicles with permanent open-diaphragm laser headlights without losses.